This invention relates to wire rope and a method of making wire rope. It is more particularly concerned with plastic impregnation of a lubricated wire rope.
Various methods are known for impregnating stranded wire rope with load-bearing plastic material in order to reduce contact stress between the strands of the rope, and improve load sharing between the strands. The plastic impregnation also serves to trap lubricant within the rope thereby improving fatigue life and providing a barrier against the ingress of abrasive and corrosive elements into the inner rope structure.
The present methods employed for the plastic impregnation of wire rope utilize dies which extrude plastic material around the rope, the diameter of the extruded plastic being nominally equal to that of the rope to be impregnated. These methods are satisfactory. However, the multiplicity of wire rope sizes, constructions and tolerances requires a broad and expensive range of tooling to assure proper finished rope diameter control. In many wire rope applications, tolerance variations are not critical. In those applications, one set of tools may be utilized on a range of rope constructions of the same diameter. However, on applications where the finished rope diameter is critical, individual tooling by rope size and construction may be required.
By the present invention a new and improved plastic impregnated wire rope and method for making the rope is proposed which will provide for more economic manufacture.
This is accomplished generally by providing a wire rope comprising generally a core containing a lubricant encapsulated by a generally cylindrical plastic jacket of greater diameter than the core and a plurality of strands laid about and embedded in said plastic jacket to provide a wire rope of a predetermined outer diameter with the plastic jacket being disposed between the strands and the outer diameter of the plastic jacket being displaced outwardly of the core and inwardly of the outer diameter of the rope. It should be noted that this rope may be constructed using a standard sized wire core and standard sized strands to produce a rope having a standard outer diameter.
In one method of making the rope the core is provided with a lubricant in the usual manner. The core is then impregnated with a thermoplastic material to provide a generally cylindrical plastic jacket of a predetermined diameter greater than the core. Thereafter, a plurality of strands is laid about the jacket, and the strands are forced radially inwardly into the jacket to form a rope of predetermined outer diameter. The strands are embedded in the plastic jacket which is flowably displaced outwardly between the strands to a location inwardly of the predetermined outer diameter of the rope.
The strands may either be embedded in the jacket solely by the application of a radially inward force or by heating the thermoplastic material prior to laying the strands about the jacket and forcing the strands radially inwardly.